High p T 0 Production in p+p, Au+Au, and d+Au Stefan Bathe UC Riverside for the Collaboration Topics in Heavy Ion Collisions McGill University, Montreal,

High pT 0 Production in p+p, Au+Au, and d+Au

Stefan Bathe

UC Riverside

for the Collaboration

Topics in Heavy Ion CollisionsMcGill University, Montreal, Canada, June 25-28, 2003

HIC03 Stefan Bathe 2

High pT Particle Production• High pT particles in

p+p and A+A– result from parton-parton

scattering with high Q2

• p+p– fragmentation of partons to

hadrons in QCD vacuum

• A+A– hard scatterings in early

stage

– high pT partons probe hot and dense nuclear matter formed in later stages

• Colored quark matter – partons lose energy via

gluon bremsstrahlung– jet quenching

– suppression of high pT

hadrons

q

q

q

q


• Charged hadrons– Drift Chamber (DC)

– Pad Chamber (PC)

PHENIX Setup• 0 via 0

– EMCal • Lead Scintillator (PbSc)• Lead Glass (PbGl)

PHENIX Central Arms ||< 0.35

• Event characterization, vertex– Beam Beam Counter (BBC)

– 3.0 < || < 3.9

– Zero Degree Calorimeter (ZDC)


p+p Collision at = 200 GeVs


• Constrains Fragmentation Function

D(Gluon-)

• Reference for Au+Au spectra

0 Production in p+phep-ex/0304038

AB hX fa/A(xa,Q

2a) fb/B(xb,Q

2b)

a b cd

Dh/c(zc,Q2

c)

• Good agreement with NLO pQCD – Factorization theorem:


Au+Au Collision at = 200 GeVNNs


Centrality Selection in Au+Au

Participants

charged particles: BBC (3.0 < | < 3.9)

spectator neutrons: ZDC (~18 m from vertex)

Spectators

• Centrality characterized by– Npart: Number of nucleons which

suffered 1 collision

– Ncoll: Number of inelastic nucleon-nucleon collisions

• Npart and Ncoll from Glauber calculations


0 Production in Au+Au

Particle

Physics

central

Nuclear

Physics

peripheral

PHENIX Collab.submitted to PRLnucl-ex/0304022

•central spectra up to 10 GeV/c

• NN-reference needed


Nuclear Modification Factor RAA• Hard processes

– yield scales with Ncoll

– reason: • small cross section

• incoherent superposition

• Nuclear Modification Factor RAA

• In the absence of nuclear effects: RAA=1 at high pT

no effect

strongsuppression

TNNAA

TAAAA

d/d

d/d0

0

pT

pNR

AATN inelNNcoll


RAA for 0 in Central Collisions

• Cronin Effect at lower energies

• Expectation– RAA > 1

• Observed– factor 4-5 suppresion

at 130 and 200 GeV

A.L.S.Angelis PLB 185, 213 (1987)WA98, EPJ C 23, 225 (2002)PHENIX, PRL 88 022301 (2002)PHENIX submitted to PRL, nucl-ex/0304022

TNNAA

TAAAA

d/d

d/d0

0

pT

pNR


Jet Quenching?

• 0 suppression described by models with parton energy loss

• Additional nuclear effects needed to describe pT dependence

• Other explanations not ruled out at this stage

q

q

q

qwithout parton energy loss

with parton energy lossWang

Wang

Levai

Levai

Vitev

Comparison with model calculations with and without parton energy loss:


Initial Final State Effects• Initial state effects

– lead to RAA 1 at high pT

– but are not related to properties of hot and dense nuclear matter

• Possibilities– Initial state multiple soft

scatterings (Cronin effect) RAA > 1

– Modifications of nuclear structure functions in nuclei (Shadowing) RAA < 1

– gluon saturation (Color Glass Condensate) RAA < 1 ?

• Final state effects– dense partonic medium

parton energy loss (and recombination)

– dense hadronic medium hadronic energy loss


d+Au: The Control Experiment

A+A collision N+A collision

• Initial state nuclear effects present in both A+A and N+A collisions

• Final state medium effects only present in A+A collisions


• No suppression in d+Au

d+Au

RAA in d+Au (RdA)

• Final state effects minimal in d+Au

• Initial state effects ruled out as explanation for suppression in Au+Au

Au+Au

d+Au


0 in d+Au: Data Theory

• Data well reproduced by – NLO pQCD calculation,

plus– phenomenological model

of Cronin effect, plus– Shadowing

Levai et al., nucl-th/0306019

Kopeliovich et al., hep-ph/0201010

Cronin Effect:

Multiple Collisions broaden high PT

spectrum


Summary

• Strong suppression of high pT particle production in central Au+Au at = 200 GeV with respect to Ncoll scaled p+p reference

• No suppression in 200 GeV d+Au• Suppression in Au+Au is caused by properties

of created hot and dense medium

NNs



Backup Slides


Centrality Dependence of Suppression

• Peripheral (60-92%) consistent with Ncoll scaling

• RAA <1 (2) for 50-60%– Npart ~ 5015

– Bjorken ~ 1.2 GeV/fm3

• Gradual or abrupt suppression not conclusive at this point

Bjorken (GeV/fm3)

D.d'EnterriaPHENIX Collab.nucl-ex/0306001


d+Au Spectra

• Final spectra for charged hadrons and identified pions.• Data span 7 orders of magnitude.


RAA vs. RdA for Identified 0

d+Au

Au+Au

Initial State Effects Only

Initial + Final

State Effects


Systematic Errors (1)

Peak extractiongeometric acc.0 reconstr. Eff.Energy scaleTrigger eff.G1 Norm. ScaleConv. Correction

Total error

pT indep.

5.0%(5.0%)

5.0%(5.0%)2.8%(2.8%)

2 GeV

3.0%(3.0%)4.0%(4.0%)4.0%(4.0%)

-

10%(10%)

6 GeV

2.0%(2.0%)4.0%(4.0%)9.0%(9.0%)

5.0%(10.0%)

14%(16%)

10 GeV

2.0%(2.0%)4.5%(4.5%)

11.0%(11.0%)3.0%(3.0%)

15%(15%)

type

ABBBBCC

PbSc (PbGl)


Charged Hadron Results

d+Au

Au+Au


First grasp at centrality selection in dAu

IR

18 m

ZDC

FCAL

p

n ZDC

Neutron tagged events areenhanced in very-peripheral collisions


First grasp at centrality selection in dAu

IR

ZDC

FCAL

p

n ZDC

FC

AL

Ene

rgy

Dep

osit


RdA / RpA

Comparison of very-peripheral events (<Ncoll>=3.6+/-0.4)

to minimum bias events (<Ncoll>=8.5+/-0.7)

Data indicates no centrality dependence

Documents

High p T 0 Production in p+p, Au+Au, and d+Au Stefan Bathe UC Riverside for the Collaboration Topics in Heavy Ion Collisions McGill University, Montreal,